Depot-level repair of in-service aircraft may involve removing skin panels and structural members. As but one example of depot-level repair, skin panels and longerons are removed from an aircraft and replaced.
During aircraft repair, an aircraft may be subjected to distortion loads such as sag, bending and twisting. To prevent distortion from occurring, the portion under repair may be secured to a large fixture via turnbuckles. The fixture is mounted to a large concrete slab.
For the most part, the fixture maintains the stiffness of the portion under repair. Still, some distortion loads may be transmitted to the portion due to imprecise adjustment of the turnbuckles. For example, some bending and twisting of a fuselage may occur after longerons are removed.